Host discrimination and ovicide by aphid hyperparasitoids Asaphes suspensus (Hymenoptera: Pteromalidae) and Dendrocerus carpenteri (Hymenoptera: Megaspilidae)

Abstract

Asaphes suspensus (Nees) and Dendrocerus carpenteri (Curtis) are common aphid hyperparasitoids that attack aphidiine primary parasitoids in mummified aphids. In this study, we investigated the self- and interspecific host discrimination and interspecific ovicidal behavior of A. suspensus and D. carpenteri. In choice tests, females of both species laid significantly more eggs on unparasitized hosts than on hosts parasitized by themselves. Interspecific host discrimination was observed in D. carpenteri, which avoided oviposition on hosts previously parasitized by A. suspensus. Asaphes suspensus, however, did not avoid oviposition on hosts parasitized by D. carpenteri. Dissection of mummies after experimental trials of interspecific discrimination revealed that damaged D. carpenteri eggs with a concave puncture site were found only when A. suspensus laid eggs on hosts parasitized by D. carpenteri. Additional observations indicated that most D. carpenteri eggs on parasitized hosts exposed to A. suspensus oviposition behavior were killed (~85 %). The apparent lack of interspecific host discrimination by A. suspensus suggests that the ovicidal ability of this species diminishes its fitness loss by multiparasitism.